Drug addiction is a chronic, relapsing disorder in which drug-related associations are capable of exerting tremendous control over behavior long after drug taking has ceased. Epigenetic modifications in the central nervous system are critical for long-term behavioral and neuronal plasticity, and have been implicated in numerous features of motivated behavior, drug-related learning, and addiction. However, our ability to harness the therapeutic potential of epigenetic manipulations in the context of addiction has been limited by the lack of detailed insight into epigenetic dynamics following drug experiences, and the inability to target specific epigenetic alterations in real time to interrogate their molecular and behaviora function. This proposal seeks to utilize single-cell whole-epigenome sequencing approaches to define epigenetic signatures of drug experience in specific neuronal populations. In addition to revealing new therapeutic candidates, this information will be directly applied to targeted epigenetic editing strategies based on CRISPR technology, which will allow manipulation of epigenetic states at specific drug-regulated genes. This novel approach will demonstrate the necessity of unique epigenetic modifications at specific genes for drug-associated behaviors, and also enable the first investigation of whether an epigenetic modification is sufficient to alte reward function. Finally, we will integrate these tools with ontogenetic approaches to enable light-driven manipulation of epigenetic states in freely moving animals. Thus, in addition to revealing the exact nature and scope of epigenetic states following drug experience, this proposal will be the first to investigate how these modifications contribute to the function of reward circuits and ultimately to reward seeking behavior in general.